Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $241.42   10.601%   $267.0129   $267.01   $267.00   $267.00  
  Purchase #2 $117.52   13.357%   $133.2171   $133.22   $133.20   $133.20  
  Purchase #3 $119.85   10.697%   $132.6704   $132.67   $132.65   $132.70  
  Purchase #4 $5.26   6.851%   $5.6204   $5.62   $5.60   $5.60  
  Purchase #5 $235.58   3.214%   $243.1515   $243.15   $243.15   $243.20  
  Purchase #6 $6.34   5.332%   $6.678   $6.68   $6.70   $6.70  
  Purchase #7 $176.25   5.475%   $185.8997   $185.90   $185.90   $185.90  
  7 purchase totals = $902.22       $974.2500   $974.25   $974.20   $974.30